The relates to an apparatus for detecting particles on a surface of semiconductor LSI wafer, photomask, magnetic bubble wafer, or the like by the use of a semiconductor laser capable of stably keeping the quantity of illumination at a predetermined intensity.
The process for detecting the contaminants or particles on wafers with a circuit pattern attached thereto in the course of manufacture of LSIs is essential for increasing the yield of the LSI products and improving reliability on the products. Automation of such detecting process has been embodied by detection methods employing polarized light illumination like those disclosed in Japanese Laid-open Patent Publication No. 55-149829 and others such as U.S. Pat. No. 4,342,515 (Japanese Laid-open Patent Publication Nos. 54-101390, 55-94145), and Japanese Laid-open Patent Publication No. 56-30630. The principle of such method will be described below with reference to FIGS. 10 to 12.
If it is only arranged to have illuminating light 4 incident on the surface of a wafer 1 at an angle of inclination .phi. as shown in FIG. 12, then reflected light 5 and scattered light 6 (FIG. 10) are produced simultaneously from the circuit pattern 2 and particles 3 respectively, and therefore, it is impossible to detect only the particles 3 discriminated from the pattern 2. So that it has been devised to detect the particles 3 by the use of a polarized laser beam.
An S-polarized laser beam 4 is arranged to illuminate a pattern 2 present on the wafer 1 as shown in FIG. 11 (a). Herein, a laser beam 4 whose electrical vector 10 is parallel with the surface of the wafer is defined as illumination by an S-polarized laser. Generally, the irregularity on the surface of the pattern 2 seen microscopically is sufficiently small as compared with the wavelength of the illuminating light and optically smooth, so that the S-polarized light 11 reflected from the pattern 2 is preserved in the reflected light 5. Therefore, if an analyzer 13 cutting the S-polarized light is inserted in the optical path of the reflected light 5, the reflected light 5 is cut off and unable to reach a photoelectric conversion element 7. On the other hand, in the scattered light 6 from the particles 3, there is included a P-polarized light 12 in addition to the S-polarized component as shown in FIG. 11 (b). This is because the surface of the particles 3 is rough, and thereby, scattered light 6 is partially polarized and the P-polarized light 12 is generated. Accordingly, if the P-polarized light 14 transmitted through the analyzer 13 is detected by the photoelectric conversion element 7, then detection of the particles 3 becomes possible.
Now, by employing two lasers 15 emitting laser beams from left and right as shown in FIG. 12, execution of stable detection of particles generating anisotropic scattered light becomes possible.
As the laser 15, the He-Ne laser has hitherto been employed in view of high and stable intensity of laser-output, long life, stable polarization characteristic, etc. However, since the He-Ne laser has a large oscillator body in size, it has been difficult to miniaturize the apparatus for detecting particles by using such a laser beam source.
Thus, because of the use of the He-Ne laser for the laser beam source as described above, there has been a problem in the prior art that miniaturization of the apparatus has not been attainable.